Some access control systems are based on an analysis of a person's biometric features in order to determine for example whether said person is authorized for access to a protected location. Said analysis of biometric features is also used in some authentication or identification systems that set out to authenticate or identify a person. This analysis is based conventionally on a comparison of biometric data collected about a person under inspection with data stored in a database.
So, for example, where access control systems are involved, biometric data on people for whom access is authorized are stored in a database. At the end of a stage of comparing data collected about a person under inspection with stored data, the system is able to determine whether said person is among those for whom access is authorized.
Biometric data is very substantially confidential in nature. Consequently, care needs to be taken to ensure said confidentiality is protected during the manipulation thereof, particularly in the interests of protecting privacy.
To this end, in the document U.S. Pat. No. 6,836,554, it is held that such biometric data are transformed by applying an irreversible transformation function thereto. Under these conditions, it is then possible for said biometric data to be manipulated in a transformed form which does not allow the original biometric data to be retrieved. Indeed, the stage that comprises comparing stored biometric data and biometric data relating to a person under inspection is then carried out on the basis of biometric data so transformed.
By proceeding in this way, even if an ill-intentioned third party intercepts said transformed biometric data, he is not able to infer the corresponding original biometric data therefrom since the transformation function which has been used is not reversible.
In this context, the greater the deformation of said biometric data caused by applying said transformation function f the higher the level of protection afforded to the confidentiality of said biometric data.
However, it should be noted that the transformed biometric data is compared in this context over the entire spatial representation of said biometric data. Consequently, such a comparison may yield spurious results where the spatial deformations caused by applying the transformation function f are too substantial. Indeed, in the case for example of biometric data relating to a face, the algorithms aimed at determining whether two deformed face images correspond to the same face may indicate that two different faces are involved, simply because said two face images have sustained deformations that are too substantial for said comparison algorithms.
In fact, in this type of biometric system, this comparison stage is an essential stage on which the reliability of a biometric system depends.
The present invention sets out to improve the situation.